John,

To me, it sounds like you have 3 issues going on.1) under powered tower speakers, 2) poorly tuned system, and 3) a short in the in-boat system putting the zx700.5 into protect mode.

My approach would be this. get what you have performing to its optimal level, then reevaluate.

For number 1, an amp change would be in order, but I would do number 2 (no pun intended) first for the tower. No matter the gear, poorly tuned is poorly tuned.

Now, for the problem with the zx700.5 going into protect mode. You are going to need to get a DVOM out and start checking speaker circuits. Also, you need to inspect real close for a possible power or ground cable shorting out at the terminal lugs on the amp. Make sure you dont have a stray strand of wire that missed the lug. Outside of shorted speaker or lead or a problem at the lugs, you could be looking at a setting/tuning issue.